The invention relates to metal-clad polymer articles comprising amorphous or fine-grained metallic coatings/layers on polymeric composite materials/substrates with good adhesion and thermal cycling performance for use in structural applications.
Due to their low cost and ease of processing/shaping by various means, polymeric materials, which are optionally filled with, or reinforced with, materials selected from the group of metals, metal alloys, and/or carbon based materials selected from the group of graphite, graphite fibers, carbon, carbon fibers and carbon nanotubes, glass, glass fibers and other inorganic fillers, are widely used.
Applying metallic coatings or layers to the surfaces of polymer parts or vice versa is of considerable commercial importance because of the desirable properties obtained by combining polymers and metals. Metallic materials, layers and/or coatings are strong, hard, tough and aesthetic and can be applied to polymer substrates by various low temperature commercial process methods including electroless deposition techniques and/or electrodeposition. The metal deposits must adhere well to the underlying polymer substrate even in corrosive environments and when subjected to thermal cycling and loads, as encountered in outdoor or industrial service.
The prior art describes numerous processes for metalizing polymers to render them suitable for metal deposition by conditioning the substrate's surface to ensure metal deposits adequately bond thereto resulting in durable and adherent metal coatings. The most popular substrate conditioning/activation process is chemical etching.
Stevenson in U.S. Pat. No. 4,552,626 (1985) describes a process for metal plating to filled thermoplastic resins such as Nylon-6®. The filled resin surface to be plated is cleaned and rendered hydrophilic and preferably deglazed by a suitable solvent or acid. At least a portion of the filler in the surface is removed, preferably by a suitable acid. Thereafter electroless plating is applied to provide an electrically conductive metal deposit followed by applying at least one metallic layer by electroplating to provide a desired wear resistant and/or decorative metallic surface. Stevensen provides no information on thermal cycling performance or adhesion strength.
Leech in U.S. Pat. No. 4,054,693 (1977) discloses processes for the activation of resinous materials with a composition comprising water, permanganate ion and manganate ion at a pH in the range of 11 to 13 exhibiting superior peel strengths following electroless metal deposition. Leech provides no information on thermal cycling performance, and adhesion strength is exclusively measured using a peel test.
Yates in U.S. Pat. No. 5,863,410 (1999) describes an electrolytic process for producing copper foil having a matte surface with micropeaks with a height not greater than about 200 microinches (˜5 micron) exhibiting a high peel strength when bonded to a polymeric substrate.
Various patents address the fabrication of articles for a variety of applications:
Erb in U.S. Pat. No. 5,352,266 (1994), and U.S. Pat. No. 5,433,797 (1995), assigned to the same applicant, describe a process for producing nanocrystalline materials, particularly nanocrystalline nickel. The nanocrystalline material is electrodeposited onto the cathode in an aqueous acidic electrolytic cell by application of a pulsed current.
Palumbo in U.S. Patent Publication No. 2005/0205425 A1 (2002) and DE 10,288,323 (2005), assigned to the same applicant, discloses a process for forming coatings or freestanding deposits of nanocrystalline metals, metal alloys or metal matrix composites. The process employs tank plating, drum plating or selective plating processes using aqueous electrolytes and optionally a non-stationary anode or cathode. Nanocrystalline metal matrix composites are disclosed as well.
Tomantschger in U.S. Ser. No. 12/003,224 (2007), assigned to the same applicant, discloses variable property deposits of fine-grained and amorphous metallic materials, optionally containing solid particulates.
Palumbo in U.S. Pat. No. 7,320,832 (2008), assigned to the same applicant, discloses means for matching the coefficient of thermal expansion (CTE) of fine-grained metallic coating to the one of the substrate by adjusting the composition of the alloy and/or by varying the chemistry and volume fraction of particulates embedded in the coating. The fine-grained metallic coatings are particularly suited for strong and lightweight articles, precision molds, sporting goods, automotive parts and components exposed to thermal cycling and include polymeric substrates. Maintaining low CTEs (<25×10−6 K−1) and matching the CTEs of the fine-grained metallic coating with the CTEs of the substrate minimizes dimensional changes during thermal cycling and preventing delamination. Palumbo provides no information on the adhesion strength.
Palumbo in U.S. Pat. No. 7,354,354 (2008), assigned to the same applicant, discloses lightweight articles comprising a polymeric material at least partially coated with a fine-grained metallic material. The fine-grained metallic material has an average grain size of 2 nm to 5,000 nm, a thickness between 25 micron and 5 cm, and a hardness between 200 VHN and 3,000 VHN. The lightweight articles are strong and ductile and exhibit high coefficients of restitution and a high stiffness and are particularly suitable for a variety of applications including aerospace and automotive parts, sporting goods, and the like. Palumbo provides no information on thermal cycling performance or adhesion strength.